The invention relates to a screw connection between rods and joint members of a three-dimensional space framework or the like, in which the rods end in tapering end pieces, which may be truncated conical pieces with a through-hole recessed axially to receive a set screw which can be threaded in and can be axially prebiased.
Known screw connections for the above purpose have a screw bolt at each end of a rod, which in turn is supported in truncated conical end pieces rotatable and axially slidable on the rod. The truncated conical end pieces are welded to the rod. To drive in the screw bolt, there is in turn a so-called key socket or drive socket, which is connected nonrotatably with the screw bolt, and on the other hand the screw bolt can also exhibit an axial movement in the drive socket. In completely assembled state the drive socket is inserted between the outside front end of a truncated conical end piece and a joint member (cf. Mengeringhausen, Raumfachwerke aus Staeben und Knoten, Bauverlag GmbH Wiesbaden and Berlin, 7th edition 1975, page 68). The screw bolt of such a connection can be thrust in axial direction by dynamic charges, which if they have a long life can develop the danger of breaking the bolt, with grave results. Indeed it is already known to bias (to lengthen) the screw bolts through the drive socket by means of a torque wrench to such a degree that the biasing force is greater than the dynamic charges being applied from the outside. Beyond a certain size of the screw connection between joint member and rod and thus a certain size of the screw bolt, however, this method is no longer suitable, on account of the relatively high torque then being applied and the reaction moment which arises as a result of the torque, which causes the joint member to be twisted. Actually it is possible to apply the requisite high torque with a so-called hydraulic wrench. These tools however are quite difficult to operate and do not work reliably on account of continually changing lever arms. Another problem of the above construction resides in that a so-called assembly hole must be present in the tubular rod for introduction of the screw bolt into the welded-on truncated conical end pieces.
A screw connection of the aforementioned structural type is already known from German Patent 3219520, in which the biasing of the screw bolt is attained by appropriate operation of special multi-part drive sockets. Each drive socket in this known solution consists of at least two parts lying one behind the other lengthwise along the screw bolt, which have screw surfaces facing one another, whereby by twisting these parts relative to one another the distance of the end surfaces of the drive socket from one another can be modified. Therefore when the parts of the drive socket are adjusted axially in opposite directions by suitable relative movement, they are pressed against the relevant joint member or rod end and with continuing relative forward movement they cause the biasing of the screw bolt. By this means it is possible to adjust this bias so that it is greater than the dynamic charges working on the screw bolt from outside. Such multi-part special drive sockets however are relatively costly and the biasing of the screw bolt by means of these drive sockets at the construction site is still relatively problematical. In addition, with this known solution the screw bolts are mounted in truncated conical end pieces, which are welded onto the ends of each one of the rods. Thus here too the aforementioned assembly hole is still required in the tubular rod.